Leukocyte migration-inhibition and humoral antibody responses (HAR) were demonstrated in swine immunized with particulate or soluble antigen of Treponema hyodysenteriae. Levamisole (at the recommended deworming level), given simultaneously with particulate vaccine did not significantly enhance nor suppress the leukocyte migration-inhibition response. However, an enhancing leukocyte migration-inhibition effect of the drug was seen in pigs given soluble vaccine in combination with levamisole compared with those receiving soluble antigen alone. Levamisole generally suppressed the HAR throughout the immunization schedule of pigs given soluble or particulate vaccine. There was no significant suppression of clinical signs of swine dysentery (SD) in animals given particulate vaccine nor in those receiving this vaccine plus levamisole. However, pigs receiving soluble vaccine plus levamisole had fewer clinical signs of SD as well as significantly fewer shedding episodes of T. hyodysenteriae than those given soluble antigen alone. When compared with the control pigs, swine vaccinated with soluble antigen had fewer days of total diarrhoea and shedding episodes of T. hyodysenteriae. However, the diarrhoea of vaccinated pigs was not significantly delayed when compared to the unvaccinated swine.